In recent years, many vehicles are provided with a navigation apparatus that provides travel guidance for the vehicle to allow a driver to easily reach a desired destination location. The navigation apparatus is a device that can detect the current position of the vehicle using a GPS receiver or the like and acquire map data corresponding to the current position from a storage medium such as a DVD-ROM or an HDD or through a network to display the map data on a liquid crystal monitor. Further, such a navigation apparatus is provided with a route calculation function for calculating an optimum route from the vehicle position to a desired destination location when the destination location is input, and adapted to set the optimum route found in the calculation as a guide route, display the guide route on a display screen, and provide audio guidance in the case where the vehicle approaches an intersection or the like in order to reliably guide a user to the desired destination location. In recent years, in addition, some cellular phones, smartphones, tablet terminals, personal computers, and so forth also have functions that are similar to those of the navigation apparatus described above.
In the navigation apparatus etc. described above, in addition, a guide route that has once been set is changed on the basis of an operation by a user. For example, International Patent Application Publication No. 2008/117712 proposes a technology in which, when a user performs a touch operation on a guide route displayed on a display and thereafter performs a drag operation, the guide route is changed to a route that passes through the end location of the drag operation by the user. The publication also discloses that the guide route is changed to a route that passes through the end location of the drag operation by the user and that least deviates from the original route.